1. Field of the Invention
The invention relates to a method for control of a diesel-engine motorization system equipped with a nitrogen oxides trap, particularly when the system is also equipped with a particle-filtration unit.
2. Discussion of the Background
By virtue of anti-pollution standards, the motorization systems of vehicles are now equipped with cleaning lines. In such a line, a nitrogen oxides trap has the purpose of capturing nitrogen oxides in the exhaust gases of an internal combustion engine. For a diesel engine, the cleaning line can be augmented by a particle filter. It even is envisioned to provide a cleaning device that integrates both functions.
As regards the operation of the nitrogen oxides trap with a diesel engine, it is known to make the engine operate cyclically in such a way that the exhaust gases are reducing agents, for purging the nitrogen oxides trap. This operation is described in European Patent 560991, for example.
During normal operation, combustion in a diesel engine takes place with excess air. Consequently, nitrogen oxides are formed, and these are captured and stored by the nitrogen oxides trap. Since the storage capacity is limited, however, it is necessary to purge the nitrogen oxides trap at regular intervals, which is achieved by the operation generating reducing gases. This operation is also known as rich-mixture operation. In this phase, the exhaust gases contain unburned hydrocarbons, carbon monoxide or hydrogen, which will react with the nitrogen oxides stored in the nitrogen oxides trap in order to eliminate them.
To achieve this operation, European Patent 560991 proposes, for example, a throttle valve in an intake conduit, so that the quantity of air admitted into a combustion chamber can be reduced and a supplementary quantity of fuel can be injected, in order that combustion takes place under rich-mixture conditions.